Biodegradable plastics filled with reinforcing materials

ABSTRACT

This invention relates to reinforced thermoplastic moulding compositions prepared from biodegradable polymers, for example aliphatic or polyester amides, aliphatic polyester urethanes, and to the use thereof for the production of mouldings and to the mouldings, wherein the reinforcing materials are selected from wood flour, fibres of natural origin, minerals of natural origin, cellulose and cellulose derivatives.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a division of application Ser. No.08/718,123, filed Sep. 18, 1996, now U.S. Pat. No. 5,827,905.

Biodegradable plastics are known (c.f. for example EP-A 561 224). It isalso known to introduce fillers into thermoplastics (c.f. for exampleRompp-Chemielexikon, 9th edition, Thieme Verlag, Germany, headword"Fullstoffe". Incorporating fillers into thermoplastics conventionallyincreases stiffness, measured by the tensile modulus of elasticity, byapproximately a factor of 2. Wood flour cannot be used as a filler inmany thermoplastics as it decomposes during processing at relativelyhigh temperatures. Glass fibres, for example, are not biodegradable anddo not number among those substances which are desired in compost once abiodegradable material has been composted. Cellulose or cellulosederivatives cannot be used as a filler in many thermoplastics as theydecompose during processing at relatively high temperatures.

The present invention provides reinforced thermoplastic mouldingcompositions prepared from biodegradable polymers, to a process for theproduction of these reinforced moulding compositions and to the use ofthe thermoplastic moulding compositions reinforced according to theinvention as biodegradable materials for the production of, for example,injection moulded articles. The mouldings are distinguished by anoutstanding range of properties, such as for example, tensile modulus ofelasticity, toughness and strength.

Biodegradable and compostable polymers which may be considered arealiphatic or partially aromatic polyesters, thermoplastic aliphatic orpartially aromatic polyester urethanes, aliphatic-aromatic polyestercarbonates, aliphatic polyester amides.

The following polymers are suitable:

Aliphatic or partially aromatic polyesters prepared from

A) linear difunctional alcohols, such as for example ethylene glycol,hexanediol or preferably butanediol and/or optionally cycloaliphaticdifunctional alcohols, such as for example cyclohexanedimethanol, and/oroptionally branched difunctional alcohols, e.g. neopentyl glycol andadditionally optionally small quantities of more highly functionalalcohols, such as for example 1,2,3-propanetriol or trimethylol propanand from aliphatic difunctional acids, such as for example and preferredsuccinic acid or adipic acid and/or optionally aromatic difunctionalacids, such as for example terephthalic acid or isophthalic acid ornaphthalenedicarboxylic acid and additionally optionally smallquantities of higher functional acids, such as for example trimelliticacid or

B) from acid- and alcohol-functionalised units, for examplehydroxybutyric acid or hydroxyvaleric acid or lactic acid, or thederivatives thereof, for example ε-caprolactone, or dilactide

or a mixture or copolymer prepared from A and B

wherein the aromatic acids constitute a proportion of no more than 50wt. %, relative to all the acids.

The acids may also be used in the form of derivatives, such as forexample acid chlorides or esters;

Aliphatic or partially aromatic polyester urethanes prepared from

C) an ester portion prepared from linear difunctional alcohols, such asfor example ethylene glycol, butanediol, hexanediol, preferablybutanediol, and/or optionally cycloaliphatic difunctional alcohols, suchas for example cyclohexanedimethanol and/or optionally brancheddifunctional alcohols, e.g. neopentyl glycol and additionally optionallysmall quantities of more highly functional alcohols, such as for example1,2,3-propanetriol, and from aliphatic difunctional acids, such as forexample succinic acid or adipic acid and/or aromatic difunctional acids,such as for example cyclohexanedicarboxylic acid and terephthalic acidand additionally optionally small quantities of more highly functionalacids, such as for example trimellitic acid or

D) from an ester portion prepared from acid- and alcohol-functionalisedunits, for example hydroxybutyric acid or hydroxyvaleric acid or lacticacid, or the derivatives thereof, for example α-caprolactone ordilactide,

or a mixture or copolymer prepared from C) and D), and

E) from the reaction product of C) and/or D) with aliphatic and/orcycloaliphatic difunctional and additionally optionally more highlyfunctional isocyanates, for example tetramethylene diisocyanate,hexamethylene diisocyanate, isophorone diisocyanate, optionallyadditionally with linear and/or branched cycloaliphatic difunctionaland/or more highly functional alcohols, for example ethylene glycol,butanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol,

wherein the ester portion C) and/or D) amounts to at least 75 wt. % andthe proportion of urethane segments amounts to at most 25 wt. %,relative to the sum of C), D) and E);

Aliphatic-aromatic polyester carbonates prepared from

F) an ester portion prepared from linear difunctional alcohols, such asfor example ethylene glycol, butanediol, hexanediol, preferablybutanediol, and/or optionally cycloaliphatic difunctional alcohols, suchas for example cyclohexanedimethanol and/or optionally brancheddifunctional alcohols, e.g. neopentyl glycol and additionally optionallysmall quantities of more highly functional alcohols, such as for example1,2,3-propanetriol or trimethylol propane and from linear difunctionalacids, such as for example succinic acid or adipic acid and/oroptionally cycloaliphatic difunctional acids, such as for examplecyclohexanedicarboxylic acid and/or optionally small amounts of brancheddifunctional acids and additionally optionally small quantities of morehighly functional acids, such as for example trimellitic acid or

G) from an ester portion prepared from acid- and alcohol-functionalisedunits, for example hydroxybutyric acid or hydroxyvaleric acid, or thederivatives thereof, for example ε-caprolactone,

or a mixture or copolymer prepared from F) and G) and

H) a carbonate portion which is produced from aromatic difunctionalphenols, preferably bisphenol A, and carbonate donors, for examplephosgene,

wherein the ester portion F) and/or G) amounts to at least 70 wt. %,relative to the sum of F), G) and H);

Aliphatic polyester amides prepared from

I) an ester portion prepared from linear and/or cycloaliphatic andadditionally optionally small amounts of branched difunctional alcoholssuch as for example ethylene glycol, butanediol, hexanediol, preferablybutanediol, cyclohexanedimethanol and additionally optionally smallquantities of more highly functional alcohols, for example1,2,3-propanetriol or trimethylol propane, and from linear and/orcycloaliphatic and additionally optionally small amounts of brancheddifunctional acids, for example succinic acid, adipic acid,cyclohexanedicarboxylic acid, preferably adipic acid, and additionallyoptionally small quantities of more highly functional acid, for exampletrimellitic acid, or

K) from an ester portion prepared from acid- and alcohol-functionalisedunits, for example hydroxybutyric acid or hydroxyvaleric acid or lacticacid, or the derivatives thereof, for example ε-caprolactone ordilactide,

or a mixture or copolymer prepared from I) and K), and

L) an amide portion prepared from linear and/or cycloaliphatic andadditionally optionally small amounts of branched difunctional andadditionally optionally small quantities of more highly functionalamines, for example tetramethylenediamine, hexamethylenediamine,isophoronediamine, and from linear and/or cycloaliphatic andadditionally optionally small amounts of branched difunctional andadditionally optionally small quantities of more highly functionalacids, for example succinic acid or adipic acid, or

M) from an amide portion prepared from acid- and amine-functionalisedunits, preferably ω-laurolactam and particularly preferablyε-caprolactam,

or a mixture prepared from L) and M) as the amide portion, wherein theester portion I) and/or K) amounts to at least 30 wt. %, relative to thesum of I), K), L) and M).

The biodegradable copolyesters, polyester carbonates, polyesterurethanes and polyester amides have a molecular weight of at least 10000g/mol and have a random distribution of the starting substances(monomers) in the polymer.

Among the stated biodegradable polymers, polyester amides, polyesterurethanes and polyester carbonates are preferred, with polyester amidesbeing particularly preferred.

The property of compostability according to the invention is defined asfollows:

The polymers to be tested are incubated at 37° C. in a liquid medium toASTM G 22 (composition in table 1) with a mixture of microorganisms fromgarden compost with swirling (200 rpm) and in the presence of air. Tothis end, approximately 1 g of the polymer in pieces of several cm insize in 250 ml of nutrient salt solution in a 1 l conical flask areinoculated with 2 ml of a suspension of 10 g of garden compost in 100 mlof nutrient salt solution. Coarse particles have previously beenscreened out of the compost suspension with a fine sieve. The dry matter(DM) content of the inoculum is then approximately 50 mg. As a controlin order to measure the abiotic weight loss of the polymer sample, abatch is combined with HgCl₂ (500 mg/l). Further control batches containcellulose (4 g/l, grade DP 500, Wolff Walsrode) in order to monitorgrowth with a natural substrate or are prepared without adding a sourceof carbon in order to determine the background growth and decrease in DMof the inoculum.

                  TABLE 1                                                         ______________________________________                                        Composition of the nutrient salt solution to ASTM G 22                        ______________________________________                                        KH.sub.2 PO.sub.4    0.7     g                                                K.sub.2 HPO.sub.4    0.7     g                                                MgSO.sub.4 --7H.sub.2 O                                                                            0.7     g                                                NH.sub.4 NO.sub.3    1.0     g                                                NaCl                 0.005   g                                                FeSO.sub.4 --7H.sub.2 O                                                                            0.002   g                                                ZnSO.sub.4 --7H.sub.2 O                                                                            0.002   g                                                MnSO.sub.4 --H.sub.2 O                                                                             0.001   g                                                Distilled H.sub.2 O  1000.0  ml                                               ______________________________________                                    

In order to determine the dry matter content of the non water solubleconstituents (polymer or polymer residues, biomass and inoculum), theentire contents of the flask is centrifuged, washed once in a 0.05 Mphosphate buffer and the insoluble residue dried at 80° C. for at least48 hours. The biomass and the pure inoculum is determined in a parallelflask. The proportion of polymer residues may be determined bysubtracting one of these measured values from the other.

Biomass is also measured by processing the entire contents of a flask.To this end, a modified version of the Lumac-3M adenosine triphosphate(ATP) determination method is used: 10 minutes after addition of thereactive reagent (Lumac), 2.5 ml of a 33% tetrabutylammonium hydroxidesolution are added. This results in the complete release of ATP from theentire biomass within 30 seconds. After this time, the ATP content maybe determined using the conventional luciferin/luciferase reaction inaccordance with Lumac's instructions. In order to correlate ATP contentwith dry matter content, a 24 hour culture of Kl. planticola is alsomeasured, the ATP/DM ratio of which has previously been determined.

For the purposes of the invention, any samples which allow a biomassgrowth on the polymer of at least 30 mg/l under the above-statedconditions within a maximum of two weeks are described as readilycompostable.

For the purposes of the invention, samples which allow a biomass growthof at most 5 mg/l under the above-stated conditions within a maximum oftwo weeks are not compostable.

Reinforcing materials are selected from the following group: wood flour,fibres of natural origin (natural fibres), minerals of natural origin,cellulose and cellulose derivatives.

For the purposes of the invention, wood flour is mechanically comminutedwood having an edge length of at most 3 mm, preferably of at most 1 mm,particularly preferably of at most 0.5 mm. There are no technicalrestrictions with regard to the type of wood, but on toxicologicalgrounds, wood flour is preferred which does not originate from oaks,beeches or tropical woods.

The thermoplastic moulding compositions generally contain 0.1 wt. % to80 wt. %, preferably 25 wt. % to 65 wt. %, particularly preferably 32wt. % to 44 wt. % of wood flour.

The present invention also provides a process for the production of thefilled or reinforced thermoplastic moulding compositions according tothe invention, characterised in that the wood flour is dried to a watercontent of at most 5 wt. %, preferably of at most 1 wt. %, andintimately mixed with the biodegradable polymer, for example in akneader or preferably an extruder.

For the purposes of the present invention, fibres of natural origin(natural fibres) which are suitable as a reinforcing material are thosehaving a minimum length of 1 mm with a length/diameter ratio of at least10. Fibres of vegetable origin are preferred, particularly preferablythe fibres of hemp, flax, ramie and sisal.

The fibres must be present in fibrous form (i.e. not clumped together asin plants) and any adhering contaminants must be removed. There is norequirement with regard to maximum length.

The thermoplastic moulding compositions generally contain 0.1 wt. % to80 wt. %, preferably 11 wt. % to 65 wt. %, particularly preferably 17wt. % to 35 wt. % of natural fibres.

The present invention also provides a process for the production of thereinforced thermoplastic moulding compositions according to theinvention, characterised in that natural fibres are dried to a watercontent of at most 5 wt. %, preferably of at most 2 wt. %, andintimately mixed with the biodegradable polymer, for example in akneader or preferably an extruder.

For the purposes of the present invention, suitable fillers are mineralsof natural origin, which are used in pulverulent form, as isconventional for incorporation into non biodegradable thermoplastics.

Examples of preferred mineral fillers are gypsum, wollastonite, andparticularly preferably chalk and kaolin.

The thermoplastic moulding compositions according to the inventioncontain 1 wt. % to 80 wt. %, preferably 10 wt. % to 65 wt. %,particularly preferably 20 wt. % to 40 wt. % of minerals of naturalorigin.

The present invention also provides a process for the production of thereinforced thermoplastic moulding compositions according to theinvention, characterised in that the minerals of natural origin areintimately mixed with the biodegradable polymer, for example in akneader or preferably an extruder.

Cellulose or cellulose derivatives are also suitable as fillers orreinforcing materials for the purposes of the invention.

For the purposes of the invention, cellulose is defined in accordancewith Rompp-Chemielexikon, 9th edition, headword "Cellulose". Celluloseis commercially available, for example, as microcrystalline celluloseunder the trade name Avicel®, from E. Merck.

For the purposes of the invention, cellulose should also be taken tomean paper flour and wood pulp (industrially processed cellulose). Paperflour is cellulose which has been processed into paper with appropriateadditives. Suitable paper flour is preferably that having constituentswith edge lengths of below 1 mm, particularly preferably of below 0.2mm.

For the purposes of the invention, cellulose derivatives are celluloseethers, such as methylcellulose, ethylcellulose,dihydroxypropylcellulose, hydroxybutylcellulose,methylhydroxyethylcellulose, methylhydroxypropylcellulose,methylhydroxybutylcellulose, ethylhydroxypropylcellulose,ethylhydroxyethylcellulose, carboxyalkylcellulose, sulphoalkylcellulose,cyanoethylcellulose, the production of which is described, for example,in Encyclopedia of polymer science and engineering, Wiley, N.Y. 1985,volume 3, pages 242 et seq. Suitable epoxides are preferablymonoepoxides, such as ethylene oxide, propylene oxide, 1,2-epoxybutane,1,2-epoxyhexane, 1,2-epoxyoctane, 1,2-epoxydecane, 1,2-epoxydodecane,1,2-epoxyhexadecane, 1,2-epoxyoctadecane, stearic acid glycidyl ether,epoxybutyl stearate, lauryl glycidyl ether, glycidyl methyl ether,glycidyl ethyl ether, glycidyl propyl ether, glycidyl butyl ether,glycidyl tert.-butyl ether, glycidyl acrylate, glycidyl methacrylate,allyl glycidyl ether, butadiene monoxide, glycidol,3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane,di-N-butylamino-2,3-epoxypropane, diethyl-2,3-epoxypropyl phosphate,4-(2,3-epoxypropyl)morpholine and styrene oxide.

Among the cellulose derivatives, cellulose ethers, such as for examplehydroxyethylcellulose or hydroxypropylcellulose, are particularlypreferred.

The thermoplastic moulding compositions generally contain 0.1 wt. % to80 wt. %, preferably 20 wt. % to 65 wt. %, particularly preferably 26wt. % to 44 wt. %, of cellulose or cellulose derivatives.

The present invention also provides a process for the production of thefilled or reinforced thermoplastic moulding compositions according tothe invention, characterised in that the cellulose or cellulosederivatives are intimately mixed with the biodegradable polymer, forexample in a kneader or preferably an extruder.

The present invention moreover provides the use of reinforcingmaterials, selected from the group comprising wood flour, fibres ofnatural origin, minerals of natural origin, cellulose and cellulosederivatives for reinforcing biodegradable plastics.

The moulding compositions according to the invention may be modifiedwith processing auxiliaries, such as for example nucleation auxiliaries,mould release agents or stabilisers, wherein care must be taken toensure that complete compostability is not impaired or that the residualsubstances in the compost, for example, mineral auxiliaries, areharmless.

The present invention also provides the mouldings, moulded parts,extrudates or foams produced from the thermoplastic mouldingcompositions according to the invention, which may be used, for example,as flower pots, plant pots, plant ties, wreath stiffeners, grave-lightsurrounds, films, profiles, coffins or coffin parts.

EXAMPLES

The polyester amide used in the Examples prepared from a proportion of60 wt. % of polycaprolactam and a proportion of 40 wt. % of an esterprepared from adipic acid and butanediol has a relative solutionviscosity of 2.5, measured on a 1% solution in meta-cresol at 20° C.

Example 1 A

60 wt. % of biodegradable polyester amide prepared from a proportion of60 wt. % of polycaprolactam and a proportion of 40 wt. % of an esterprepared from adipic acid and butanediol are compounded at a rate of 10kg/h with 40 wt. % of wood flour in a Brabender DSE 32 twin screwextruder at a speed of 150 rpm and a melt temperature of 209° C. andthen injection moulded to produce test specimens.

Testing reveals a tensile modulus of elasticity of 1505±16 N/mm²,measured to DIN 53 457, and an impact strength of 28.2±1.5 kJ/m²,measured to ISO 180-1C.

Example 1 B

65 wt. % of biodegradable polyester amide according to Example 1A arecompounded with 35 wt. % of wood flour on a twin screw extruder ZSK32/14 at a rate of 10 kg/h at a speed of 150 rpm and a melt temperatureof 178° C. and injection moulded to produce test specimens.

Testing reveals a tensile modulus of elasticity of 1410±2 N/mm²,measured to DIN 53 457, and an impact strength of 40.6±10.2 kJ/m²,measured to ISO 180-1C.

Example 2

70 wt. % of biodegradable polyester amide prepared from a proportion of60 wt. % of polycaprolactam and a proportion of 40 wt. % of an esterprepared from adipic acid and butanediol (relative solution viscosity:2.5, measured on a 1% solution in meta-cresol at 20° C.) are compoundedwith 30 wt. % of hemp fibres on a ZSK 32/14 twin screw extruder at arate of 5.5 kg/h and a melt temperature of 176° C. and then injectionmoulded to produce test specimens.

Testing reveals a tensile modulus of elasticity of 1112±19 N/mm²,measured to DIN 53 457, and an impact strength of 52.2±5.2 kJ/m²,measured to ISO 180-1C.

Example 3 A

(according to the invention)

60 wt. % of biodegradable polyester amide prepared from a proportion of60 wt. % of polycaprolactam and a proportion of 40 wt. % of an esterprepared from adipic acid and butanediol are compounded with 40 wt. % ofkaolin in a ZSK 32/14 twin screw extruder at a rate of 10 kg/h and amelt temperature of 168° C. and then injection moulded to produce testspecimens.

Testing reveals a tensile modulus of elasticity of 599±70 N/mm²,measured to DIN 53 457, and an impact strength of "unbroken", measuredto ISO 180-1C.

Example 3 B

50 wt. % of biodegradable polyester amide prepared from a proportion of60 wt. % of polycaprolactam and a proportion of 40 wt. % of an esterprepared from adipic acid and butanediol are compounded with 50 wt. % ofkaolin in a ZSK 32/14 twin screw extruder at a rate of 10 kg/h and amelt temperature of 170° C. and then injection moulded to produce testspecimens.

Testing reveals a tensile modulus of elasticity of 716±74 N/mm²,measured to DIN 53 457, and an impact strength of "unbroken", measuredto ISO 180-1C.

Example 4 A

Biodegradable polyester amide prepared from a proportion of 60 wt. % ofpolycaprolactam and a proportion of 40 wt. % of an ester prepared fromadipic acid and butanediol is compounded at a rate of 10 kg/h with 40wt. % of microcrystalline cellulose (Avicel®, E. Merck) in a ZSK 32/14twin screw extruder at a speed of 150 rpm and a melt temperature of 174°C. and then injection moulded to produce test specimens.

Testing reveals a tensile modulus of elasticity of 1030 N/mm², measuredto DIN 53 457, and an impact strength of 33.0 kJ/m², measured to ISO180-1C.

Example 4 B

Biodegradable polyester amide prepared from a proportion of 60 wt. % ofpolycaprolactam and a proportion of 40 wt. % of an ester prepared fromadipic acid and butanediol is compounded at a rate of 10 kg/h with 50wt. % of microcrystalline cellulose (Avicel®, E. Merck) in a ZSK 32/14twin screw extruder at a speed of 150 rpm and a melt temperature of 177°C. and then injection moulded to produce test specimens.

Testing reveals a tensile modulus of elasticity of 1689 N/mm², measuredto DIN 53 457, and an impact strength of 22.0 kJ/m², measured to ISO180-1C.

Example 5

Biodegradable polyester amide prepared from a proportion of 60 wt. % ofpolycaprolactam and a proportion of 40 wt. % of an ester prepared fromadipic acid and butanediol is compounded with 40 wt. % ofhydroxypropylcellulose and then injection moulded to produce testspecimens.

Testing reveals a tensile modulus of elasticity of 1420 N/mm², measuredto DIN 53 457.

Comparison 6

Test specimens made from pure polyester amide prepared from a proportionof 60 wt. % of polycaprolactam and a proportion of 40 wt. % of an esterprepared from adipic acid and butanediol (relative solution viscosity:2.5, measured on a 1% solution in meta-cresol at 20° C.) have a tensilemodulus of elasticity of 200 N/mm² (measured to DIN 53 457) and animpact strength of "unbroken" (measured to ISO 180-1C).

What is claimed is:
 1. Reinforced thermoplastic moulding compositionscontaining aliphatic polyester amides, and wherein the aliphaticpolyester amides have a random distribution of starting substance andhave a molecular weight of at least 10,000 g/mol, and reinforcingmaterials selected from the group consisting of fibers of natural originand cellulose ethers.
 2. Reinforced thermoplastic molding compositionsas in claim 1 wherein the cellulose ethers are selected from the groupconsisting of methylcellulose, ethylcellulose, dihydroxypropylcellulose,hydroxybutylcellulose, methylhydroxyethylcellulose,methylhydroxypropylcellulose, methylhydroxybutylcellulose,ethylhydroxypropylcellulose, ethylhydroxyethylcellulose,carboxyalkylcellulose, sulphoalkylcellulose, and cyanoethylcellulose. 3.Reinforced thermoplastic molding compositions as in claim 1 wherein thecellulose ethers are selected from the group consisting ofhydroxyethylcellulose and hydroxypropylcellulose.
 4. Reinforcedthermoplastic molding compositions as in claim 1 wherein the fibers ofnatural origin comprise fibers of vegetable origin.
 5. Reinforcedthermoplastic molding compositions as in claim 4 wherein the fibers ofvegetable origin are selected from the group consisting of hemp, flax,ramie and sisal fibers.
 6. Reinforced thermoplastic molding compositionsas in claim 1 wherein the fibers of natural origin having minimum lengthof 1 mm with a length to diameter ratio of at least 10.